Various attempts have been made to obtain an olefin polymer of which the primary structure, the molecular weight or the like are controlled by changing variously the structure of a metallocene complex structure (Patent Documents 1 and 2, Non-Patent Documents 1 and 2). Of the structures of a metallocene complex, the effect of symmetry of a metallocene complex (racemic-form (C2 symmetric), meso-form (Cs symmetric) exerted on the polymerization performance is significantly large. Therefore, studies are made on the synthesis or evaluation of polymerization performance of a metallocene complex having symmetry (Non-Patent Documents 3 and 4).
However, in the case of mono-cross-linked metallocene complex, a mixture of a racemic body and a meso body is obtained when a complex is synthesized. Therefore, various industrially inadvantageous steps, such as separation by re-crystallization, use of specific raw materials, use of an auxiliary reagent in the presence of light or the like, are required (Patent Documents 3-5).
On the other hand, in the case of a double-cross-linked metallocene complex, it is expected to obtain a theoretically pure raceme or meso body, and hence, various studies have been made. For example, in Non-Patent Document 5, various ethylene-double-cross-linked metallocene complexes are obtained as a pure raceme body. However, since multi-stage reaction steps are required, the yield thereof is significantly small.
Patent Documents 6 and 7 each disclose a method for producing a double-cross-linked metallocene complex having a silicon atom-containing cross-linking group. Specific polymerization performance has been found. However, in the case of a double-cross-linked metallocene complex having a silicon atom-containing cross-linking group, in addition to an intended meso-form ligand, another symmetric ligand (racemic-form) may be mixed in as an isomer. Therefore, in order to obtain an intended symmetric double-cross-linked metallocene complex, steps become complicated since washing that needs a large amount of an organic solvent or re-crystallization is required. In addition, since there is a problem that the yield of the complex is significantly reduced, industrial production of the complex is not realistic.
Further, due to the above-mentioned problems, it was difficult to find new functions in olefin polymerization by variously changing the structure of the meso-form double-cross-linked metallocene complex.
In association with this problem, Non-Patent Documents 6 to 8 each report an isomerization reaction of a double-cross-linked complex having a silicon-containing group.
As mentioned above, although a method for producing selectively a meso-form of a double-cross-linked complex having a silicon-containing group as a cross link has been required, an effective method has not yet been found.
Further, as for a racemic-form, the racemic-form double-cross-linked metallocene complex which was reported in the past has a low yield. Therefore, when polyolefin is produced on the industrial basis, there is a defect that the cost of a catalyst was high. For example, Bercaws or the like synthesized a Cp-based racemic-form dimethylsilylene-double-cross-linked metallocene-complex. Since the double-cross-linked complex as a raw material is a mixture of a meso form and a racemic-form, the racemic-form is separated by washing. Therefore, the yield of the double-cross-linked complex is as small as about 30% (Non-Patent Document 9).
Brintzinger et al obtained a racemic-form double-cross-linked ligand and a racemic-form double-cross-linked metallocene complex by utilizing a racemization reaction which proceeds from a meso-form double-cross-linked ligand. However, racemization does not proceed completely, and since only about 20 to 40% of a meso-form double-cross-linked metallocene complex is mixed in, purification by re-crystallization is required in order to obtain a raceme complex. The final yield of the racemic-form double-cross-linked metallocene complex is significantly small (Non-Patent Document 8).
Patent Documents 8 and 9 each study a double-cross-linked metallocene complex having an indene skeleton. Unlike the above-mentioned example, although a double-cross-linked ligand of a highly-pure racemic-form containing no meso form is obtained, the yield thereof is as low as 30 to 40%. In these documents, a double-cross-linked ligand is produced by coupling Ind-SiMe2Cl as a raw material. This reaction is a complex reaction which yields other product than intended products, and hence, the yield is thought to be small.